The superhard materials diamond and cubic boron nitride (hereinafter sometimes referred to as CBN) have a wide variety of abrasive and cutting tool uses as well as uses which do not involve the relatively high impact forces incident to grinding and sawing operations. Thus, in applications in which wear resistance is of primary concern such as in conduits for the delivery of sprays of abrasive materials, the matrix of bonding medium may be much more brittle than the impact-resistant resin and metal bonding media generally used. Because of their superior hardness, silicon and silicon-base alloys are preferred as sources of the bonding medium in the fabrication of conduits made of these superhard materials. Efforts heretofore to produce strong and well-bonded compacts (i.e., bonded polycrystalline bodies) of CBN by infiltrating a particulate mass of CBN with molten silicon or an alloy thereof have, however, been unsuccessful, but for one notable exception. That exception is the invention disclosed and claimed in U.S. Pat. No. 4,220,455, assigned to the assignee hereof, in accordance with which superhard particles are given a coating of non-diamond carbon prior to contacting them with molten silicon or silicon-base alloy. Both in the case of diamond particles and that of CBN particles, the non-diamond carbon reacts with molten silicon to form silicon carbide which serves to bond the particles in the resulting mass of metal or alloy, the superhard material ranging in volume from about 1% to 80% of the resulting composite body, according to intended use requirements.